Device for attenuating the pitching of an engine-driven vehicle

ABSTRACT

The invention relates to a device for damping the pitching of an engine-driven vehicle with a chassis and axles  5,  at least one of which is mounted fixedly on the chassis. The aim of the invention is to provide a simplified corresponding device. To this end, the torque of at least one wheel borne on the axles ( 5 ) is influenced on the basis of the size of the pitching in such a way that the pitching is damped.

[0001] The invention concerns a device for damping the pitching of anengine-driven vehicle with a chassis and axles, of which at least one isfixed rigidly on the chassis, and with flexible tyres.

[0002] In connection with vehicles having axles mounted fixedly(unflexibly) on the chassis, like construction machines, forestmachines, agricultural machines, skid-steered loaders, caterpillartractors with pneumatic tyres and similar vehicles, the upper part ofthe vehicle, when driving, usually performs pitching, that is,oscillating movements, around an axis, which is parallel to the axles.The frequency and the amplitude of the pitching depend on the speed andthe load of the vehicle.

[0003] The reason for the pitching is that the axles are mounted fixedlyon the vehicle chassis, meaning that the only flexibility comes from thepneumatic tyres.

[0004] In order to damp the pitching of a vehicle with a working deviceoperated by a hydraulic cylinder, it is known either to insert a cushionfor the boom cylinder in the hydraulic system (U.S. Pat. No. 5,195,864)or to control the oil supply to the hydraulic cylinder and thus also therelative position of the working device (U.S. Pat. No. 5,897,287). Inorder to damp the pitching of a tractor, for example when driving in theroads with mounted plough, it is further known (EP 0 518 226 A1) toprovide the front axle with an active damping in the form of a dampingcylinder, which counteracts the pitching.

[0005] Influencing the steering of the working device in order to remedypitching would also influence the desired movement of the working deviceduring operation. The insertion of an additional damping cylinder isexpensive.

[0006] The invention is based on the task of providing a device fordamping the pitching of an engine-driven vehicle, which does not requireinfluences on the steering of a possible working device and which has asimple design.

[0007] According to the invention, this task is solved in that thetorque of at least one of the wheels supported on the axles can beinfluenced, in dependence of a measure of the pitching of the vehicle,in such a way that the pitching is damped.

[0008] Preferably, it is ensured that one of the following entitiesserves as measure of the pitching:

[0009] the operating pressure of at least one hydraulic engine drivingat least one of the axles,

[0010] the torque of at least one electric or combustion engine drivingat least one of the axles,

[0011] the pressure or the piston position in a working cylinder,particularly the boom cylinder, of a working device mounted on thevehicle,

[0012] the tyre pressure, or

[0013] the angular acceleration of a vehicle part around the pitchingaxis.

[0014] Thus, the torque of at least one of the wheels can be influencedby a change of

[0015] the torque of a driving engine of at least one axle,

[0016] the operating voltage or the operating frequency of an electricdriving engine of at least one axle,

[0017] the gear ratio of a gear transmission between driving engine(s)and axle(s) or

[0018] the braking power of at least one brake of a braking system ofthe vehicle.

[0019] In the following the invention and its various embodiments areexplained in detail on the basis of the enclosed drawings showingpreferred embodiments:

[0020]FIG. 1 a block diagram of the principal design of a deviceaccording to the invention,

[0021]FIG. 2 a more detailed schematic view of an embodiment of a deviceaccording to the invention,

[0022]FIG. 3 a more detailed schematic view of another embodiment of adevice according to the invention,

[0023]FIG. 4 a more detailed schematic view of a further embodiment of adevice according to the invention,

[0024]FIG. 5 schematic views of a vehicle, whose upper part performspitching, and

[0025]FIG. 6 various curve diagrams illustrating the idea of theinvention

[0026] According to FIG. 1, a sensor 1 provides a measurement of thepitching of a vehicle part 2 of a vehicle with a chassis and axles, ofwhich at least one is mounted fixedly on the chassis, and which hasflexible tyres, preferably pneumatic tyres, and in dependence of theoutput signal of the sensor 1, the torque of at least one wheel 4 of thewheels supported on the axles is influenced by a steering 3 in such away that the pitching is damped.

[0027] This is based on the knowledge that during braking the upper partof a vehicle endeavours to perform a movement in the travellingdirection in relation to the axles, and during acceleration itendeavours to perform the opposite movement. Each of these movementsalso corresponds to a half cycle of a pitching movement. When increasingthe torque of at least one wheel in the travelling direction during ahalf cycle of a pitching movement in the travelling direction, and viceversa, each half cycle of a pitching movement can be damped, until allpitching movements have substantially subsided.

[0028] For this purpose, a measure of the pitching is determined. Forexample, one of the following entities can be used as measure of thepitching: the operating pressure of at least one hydraulic enginedriving at least one of the axles, the torque of at least one electricor combustion engine driving at least one of the axles, the pressure orthe piston position in a working cylinder, particularly the boomcylinder, of a working device mounted on the vehicle, the tyre pressure,and the angular acceleration of a vehicle part around the pitching axis.

[0029] In dependence of the measure of the pitching, the torque of atleast one of the wheels is changed with the purpose of damping thepitching, for example, by influencing the torque of a driving engine ofat least one axle or the operating voltage or the operating frequency ofan electric driving engine of at least one axle or the gear ratio of agear transmission between driving engine and axle or several drivingengines and axles, or the braking power of at least one brake of abraking system of the vehicle.

[0030]FIG. 2 shows a schematic view of a first example of determiningthe measure of pitching and the influencing of the torque of a drivenwheel. The wheel, not shown in FIG. 2, is mounted unrotatably on an axle5, which can be driven by a hydraulic engine 6 with two flow directions.A hydraulic pump 7 with variable displacement volume and two flowdirections, which is driven by a not shown combustion engine, controlsthe driving pressure of the hydraulic engine 6. The displacement volumeof the pump is determined by an electromagnetic regulating unit 8 independence of a control signal of an electronic control part 9 of thecontrol 3, which converts the measuring signal of a sensor 1, convertingthe pressure in a line 10 connecting the hydraulic engine 6 and thehydraulic pump 7, into the control signal of the regulating unit 8. Forexample, the control signal of the regulating unit 8, generated via theelectronic control part 9, can represent the amplitude of a pitching orthe angle acceleration of the vehicle part 2, as the pressure in theline 10 is a measure of the oscillation width of the pitching, that is,the angle of the rotary movement of the upper vehicle part around thepitching axis, lying between the axles, above their common level andparallel to the axles. On the basis of this oscillation angle or rotaryangle of the upper vehicle part, the angle speed or angle accelerationcan then be calculated in the electronic control part 9. The controlsignal of the control part 9 then adjusts the displacement of thehydraulic pump 7 in each half wave of the pitching in such a way thatthe change of the pressure in the line 10, caused by this adjustment, isdirected opposite to the change of the pressure in line 10 occurringduring each half wave of the pitching. In other words, when the pressurein the line 10 increases because of a half wave of the pitching, theelectronic control part 9 causes a reduction of the displacement of thehydraulic pump 7 via the regulating unit 8, and when the pressure in theline 10 is reduced by the following, oppositely directed half wave ofthe pitching, the pressure in the line 10 is increased via the hydraulicpump 7. Thus, in the cause of a few oscillations, the pitching issubstantially damped.

[0031] In the embodiment according to FIG. 3, parts corresponding tothose in FIG. 2 have the same reference numbers. The vehicle is providedwith a working device 11, which again is provided with a workingcylinder 13 for activating the working device 11 and a directionalcontrol valve 14 for the manual control of the working cylinder 13 via ahydraulic control part 12. On a line 15, which connects the workingcylinder 13 with the directional control valve 14, which is connectedwith a hydraulic pump (not shown), the sensor 1 is connected. In theelectronic control part 9, the electric output signal of the sensor 1 isconverted to an electric control signal for a throttling electromagnetic2/2-way valve 16, which is connected between the lines 10 and 17connecting the hydraulic engine 6 with the hydraulic pump 7. Thedisplacement of the hydraulic pump 7 and the flow direction in thehydraulic pump 7 are adjustable by a manually operated regulating unit18. When the upper vehicle part 2 performs pitching, this usually alsocauses pressure fluctuations in the line 15, particularly when theworking device 11 is a heavy device, for example a digging tool for abackhoe. These pressure fluctuations are again measured by the sensor 1and converted by the electronic control part 9 into an electricalcontrol signal for the 2/2-way valve 16. A pressure increase in the line15, which also causes a pressure increase in the line 10, will switchthe 2/2-way valve 16 from the shown locked position to the open positionfor the duration of the pressure increase, so that the hydraulic pump 7and the hydraulic engine 6 are short-circuited. Thus, also the pressurein the hydraulic engine 6 is decreased, so that a pressure equalising isachieved. A pressure drop in the lines 10 and 15, caused by a pitchinghalf wave in the opposite direction, will switch the 2/2-way valve backinto the locked position and increase the pressure in the line 10 bymeans of the hydraulic pump 7, so that also with this embodiment thepitching will subside after a short while.

[0032] In the embodiment according to FIG. 4, the parts corresponding tothose in the preceding embodiments have the same reference numbers. Theembodiment according to FIG. 4 differs from that in FIG. 1 in thatinstead of one hydraulic engine 6, it has an additional hydraulic engine19 driving the same axle 5 and that an electromagnetically activated4/2-way valve 20 is connected between the lines 10 and 17. When thepressure in the line 10 varies due to pitching, which is transferred tothe axle 5 and from there to the pressure in the line 10 via thehydraulic engines 6, 19, the electronic control part 9 will, in the caseof an increase in the pressure, cause a switching of the 4/2-way valvefrom the open position shown to the closed position, in which thehydraulic engine 6 is turned off, and only the hydraulic engine 19 ison. Accordingly, the torque transferred to the axle 5 is reduced. Thepressure drop in the line 10 during the next half wave of the pitchingwill switch the 4/2-way valve back to the open position shown, causingthe torque on the axle 5 and thus also the torque on the wheel on thisaxle 5 to increase. This process is repeated until after a short whilethe pitching has substantially subsided.

[0033] By means of different schematic views of a vehicle 21 (FIGS. 5(A)to 5(C)), whose upper part 22 performs pitching around a transversalaxis 23, and a diagram (FIG. 5(D)) of the pitching angle p withoutdamping of the upper part 22 of the vehicle 21 at different times, t₀,t₁ and t₂ in dependence of the time t, FIG. 5 shows, in FIG. 5(E), theundamped oscillations of the torque M of, for example, the axis 5 andthe wheel 4 fitted on said axis, corresponding to the oscillations ofthe rotating angle φ, and, in FIG. 5(F), the damped oscillations of thetorque M of the axle 5 and the wheel 4 fitted on said axle, which resultfrom the short, small torque impulses M_(i) effected in each half waveof the oscillations of the torque M according to FIG. 5(E), by thedevice according to the invention, in the opposite direction of theoscillation half waves caused by the pitching. The torque impulses M₁compensating the torque oscillations cause an eventual subsiding of theoscillations of the torque M or the pitching, respectively, to a smallremaining oscillation width.

[0034] When a longer duration of the subsiding of the pitching ispermissible or sufficient, the compensating (oppositely directed) torqueimpulses M₁ can also be affected only in every second half wave of thepitching.

[0035] Further variations of the embodiments shown could be, forexample, that, instead of the hydraulic control part for the axle or forthe wheel 4 fitted on said axle, respectively, an electrical drivingengine with controllable torque, for example a brushless d.c.-engine,whose torque is measured by a sensor and is controlled by means of acontrol part, for example with an inverter, whose output voltage orfrequency is controllable by means of the output signal of the sensor,in such a way that pitching is damped.

[0036] Accordingly, also the gear ratio of a gear transmission betweendriving engine and axle, for example when using a combustion engine, canbe changed in such a way that the pitching is damped.

[0037] Further, it is possible to change the braking force of at leastone brake in a braking system of the vehicle in dependence of the sizeof the pitching in such a way that the pitching is damped.

[0038] With vehicles, such as backhoe or surface excavators, whosewheels, arranged on either side of the vehicle, are driven by their ownengine via a chain drive, for example a skid steered loader, each of thetwo driving engines can also be controlled in dependence of the size ofthe pitching in such a way that the pitching is damped.

1. Device for damping the pitching of an engine-driven vehicle with achassis and axles, of which at least one is mounted fixedly on thechassis, and with flexible tyres, characterised in that the torque of atleast one of the wheels (4) supported on the axles (5) can be influencedin dependence of a measure of the pitching of the vehicle (21) in such away that the pitching is damped.
 2. Device according to claim 1,characterised in that one of the following entities serves as measurefor the pitching: the operating pressure of at least one hydraulicengine (6, 19) driving at least one of the axles (5), the torque of atleast one electric or combustion engine driving at least one of theaxles, the pressure or the piston position in a working cylinder (13),particularly the boom cylinder, of a working device (11) mounted on thevehicle (21), the tyre pressure, or the angular acceleration of avehicle part (2, 22) around the pitching axis (23).
 3. Device accordingto claim 1 or 2, characterised in that the torque of at least one of thewheels (4) can be influenced by a change of the torque of a drivingengine (6, 19) of at least one axle (5), the operating voltage or theoperating frequency of an electric driving engine of at least one axle(5), the gear ratio of a gear transmission between driving engine(s) andaxle(s) or the braking power of at least one brake of a braking systemof the vehicle.